Antiferromagnetic Exchange Interactions Research Articles

A Nanosized {NiII18} Cluster with a 'Flying Saucer' Topology Exhibiting Slow Relaxation of Magnetisation Phenomena at Both 15 K and 1.3 K.

A high-nuclearity {Ni18} complex (1) with a unique 'flying saucer' motif has been prepared from the organic chelate, α-methyl-2-pyridine-methanol (mpmH), in conjunction with bridging azido (N3-) and peroxido (O22-) ligands. Magnetic susceptibility measurements revealed the presence of both ferro- and antiferromagnetic exchange interactions between the metal centres in 1, and the stabilization of spin states with appreciable S values at two different temperature regimes. The end-on bridging azido and alkoxido groups are in all likelyhood the ferromagnetic mediators, while the η3:η3:μ6-bridging peroxides most likely promote the antiparallel alignment of the metals' spin vectors, yielding an overall non-zero spin ground state for the centrosymmetric compound 1. Furthermore, the {Ni18} nanosized cluster behaves as a single-molecule magnet, exhibiting magnetic hysteresis at low temperatures and two relaxation processes at 15 K and 1.3 K, a very rare phenomenon in polynuclear magnetic 3d-metal clusters.

Room-Temperature Ferromagnetism with Strong Spin-Orbit Coupling Achieved in CaRuO3 Interfacial Phase via Magnetic Proximity Effect.

Recently, theoretical and experimental research predicted that ferromagnets with strong spin-orbit coupling (SOC) could serve as spin sources with dramatically enhanced spin-orbit torque (SOT) efficiency due to the combination of spin Hall effect and anomalous Hall effect (AHE), presenting potential advantages over conventional nonmagnetic heavy metals. However, materials with a strong SOC and room-temperature ferromagnetism are rare. Here, we report on a ferromagnetic (FM) interfacial phase with Curie temperature exceeding 300 K in the heavy transition-metal oxide CaRuO3, in proximity to La0.67Sr0.33MnO3. Electron energy loss and polarized neutron reflectometry spectra reveal the strong charge transfer from Ru to Mn at the interface, triggering antiferromagnetic exchange interactions between interfacial Ru/Mn ions and thus transferring magnetic order from La0.67Sr0.33MnO3 to CaRuO3. An obvious advantage of such interfacial phase is the enhanced anomalous Hall effect at temperatures from 150 to 300 K. Compared to the most promising room-temperature ferromagnetic oxide La0.67Sr0.33MnO3, the anomalous Hall conductivity σxyAHE (or anomalous Hall angle θH) of CaRuO3/La0.67Sr0.33MnO3 superlattices is increased by 30 (or 31) times at 150 K and 10 (or 3) times at 300 K. This work demonstrates a special approach for inducing ferromagnetism in heavy transition-metal oxides with strong SOC, offering promising prospects for all-oxide-based spintronic applications.

A Structure and Magnetism Study of {MnII3MnIVLnIII3} Coordination Complexes with Ln = Dy, Yb

We report the research results of polynuclear complexes consisting of 3d-4f mixed-metal cores that are maintained by acetate ligands and multidentate Schiff base ligands with structurally exposed thioether groups. The presence of the latter at the periphery of these neutral compounds enables their anchoring onto substrate surfaces. Specifically, we investigated the electronic and magnetic properties as well as the structural arrangement in {MnII3MnIVLnIII3} with Ln = Dy, Yb coordination complexes using various complementary methods. We studied the electronic and atomic structure of the target compounds using the XAS and XES techniques. The molecular structures of the compounds were determined using density functional theory, and the magnetic data were obtained as a function of the magnetic field. Using the XMCD method, we followed the changes in the electronic and magnetic properties of adsorbed magnetic compounds induced by the reaction of ligands through interaction with the substrate. The complexes show antiferromagnetic exchange interactions between Mn and Ln ions. The spectroscopic analyses confirmed the structural and electronic integrity of complexes in organic solution. This study provides important input for a full understanding of the dependence of the magnetic properties and the molecule–substrate interaction of single adsorbed molecules on the type of ligands. It highlights the importance of chemical synthesis for controlling and tailoring the magnetic properties of metalorganic molecules for their use as optimized building blocks of future molecular spin electronics.

Magnetic and magnetocaloric dynamics in [formula omitted] double perovskites: Impact of A and B site variations analyzed through Monte Carlo simulation and Ab initio calculations

We investigate the magnetic and magnetocaloric properties of the double perovskites Sr2FeOsO6,Sr2FeCoO6,Dy2FeOsO6 and Dy2FeCoO6 using a combination of Monte Carlo simulations and Density Functional Theory (DFT). The exchange couplings were calculated using DFT. Sr2FeOsO6 exhibits antiferromagnetic ordering with two transitions at 50 and 150 K, driven by strong antiferromagnetic exchange interactions between Fe³⁺ and Os⁵⁺ ions. In contrast, Sr2FeCoO6 shows ferrimagnetic behavior with a single transition around 75 K, attributed to ferromagnetic coupling between Co2⁺ and Fe³⁺ ions. For the rare-earth-containing compounds, Dy2FeOsO6 demonstrates complex magnetic ordering with transitions at approximately 20 K and 140 K, influenced by the strong spin-orbit coupling of Dy³⁺ ions. Similarly, Dy2FeCoO6 exhibits two transitions at around 60 K and 170 K, reflecting a mix of ferromagnetic and antiferromagnetic interactions involving Dy³⁺, Co2⁺, and Fe³⁺ ions. Sr2FeOsO6 shows a peak magnetic entropy change ΔSm of 0.22 J/kg.K under a 5 T field at 50 K, while Sr2FeCoO6 exhibits a broader peak at 75 K with ΔSm of 1.5 J/kg·K. Dy2FeOsO6 presents significant ΔSm peaks at 20 K and 140 K, reaching 1.9 J/kg·K under a 5 T field. Dy2FeCoO6 displays the highest ΔSm of 4.0 J/kg·K at 60 K.

Synthesis, crystallographic, spectroscopic, magnetic, and DFT characterization of a new strandberg-type polyoxometalate: (H2AEP)4[CoP2Mo5]2 ̶ first principles calculations

This work reports the synthesis of a novel diphosphopentamolybdate compound with the formula (C6H17N3)4[Co(H2O)4P2Mo5O23]2‧8·74H2O abbreviated as (H2AEP)4[CoP2Mo5]2. Characterization of this compound was carried out using various techniques, including X-ray diffraction, thermal analysis (TGA), and spectroscopies such as FT-IR, Raman, UV–visible, and fluorescence. The structural study reveals that the studied material crystallizes in the orthorhombic system Pca21 with lattice parameters of a = 18.6348(16) Å, b = 11.8613(10) Å, c = 35.074(3) Å, and volume V = 7752.5(11) Å3, and a number of formula units per primitive cell Z = 4. The crystal structure study reveals that the Strandberg anions (P2Mo5O23)6− are connected to Co(II) octahedra through the terminal oxygen atoms of the PO4 tetrahedra, creating 1-D anionic chains in the crystallographic direction [101]. The 1-(2-Aminoethyl)piperazinium (AEP) cations are located within the anionic framework to neutralize its negative charge. The magnetic characteristics of the compound were investigated by examining the temperature-dependent molecular susceptibility over the range of 2–300 K. The analysis revealed the presence of an antiferromagnetic exchange interaction. Moreover, the material's refractive index exhibited significant dispersive behavior within the visible spectrum, indicating its potential for use in visible optical communication devices. A first-principles density functional theory (DFT)-based computational study confirms the semiconducting behavior of (H2AEP)4[CoP2Mo5]2, revealing that in the ground state, high-spin octahedrally coordinated Co2+ cations exhibit a very weak antiferromagnetic coupling along the [Co(H2O)4P2Mo5O23]∞4−chains running in the crystal a direction.

A prediction of high temperature magnetic coupling in transition metal phthalocyanines.

In spintronics, a perennial goal has been the generation of organic spin-bearing semiconductor materials with magnetic ordering stable at room temperature. To this end, the class of transition metal phthalocyanines has shown much promise in fulfilling this ambition. In particular, alpha-phase cobalt (II) phthalocyanine (α-CoPc) exhibits strong antiferromagnetic exchange interactions producing a long range order up to ∼100K. However, the underlying mechanism by which this magnetic interaction proceeds is not well understood. In this report, a simple mechanism has been proposed based on the Hubbard Hamiltonian, which elucidates the exchange coupling in α-CoPc. The mechanism provides stipulations for increasing the magnetic coupling, and this directs to a proposal that substitution of the central cobalt ion for rhodium will lead to a significant increase in coupling strength. The strength of this exchange interaction has been evaluated using broken symmetry hybrid exchange density functional theory and indicates that the novel rhodium (II) phthalocyanine system is indeed predicted to exhibit significantly stronger magnetic ordering. This study, therefore, identifies the coupling mechanism in α-CoPc as primarily attributable to kinetic exchange, explains its previously reported strong coupling relative to its first-row transition metal counterparts, and suggests that rhodium (II) phthalocyanine is likely to exhibit stable magnetic ordering at room temperature.

Antiferro skyrmion crystals consisting of skyrmions and anti-skyrmions on a bilayer square lattice

An antiferro-type skyrmion crystal consisting of skyrmions with a negative topological charge and antiskyrmions with a positive topological charge manifests itself in its peculiar topological magnetism. We theoretically investigate the emergence of such an antiferro-type skyrmion crystal, where the topological charge exists in each sublattice but vanishes in the whole system. By performing the simulated annealing for an effective spin model with competing exchange interactions and staggered Dzyaloshinskii-Moriya interaction in momentum space on a bilayer square lattice, we find that the synergy between the antiferromagnetic interlayer exchange interaction and high-harmonic wave-vector interaction in addition to the staggered Dzyaloshinskii-Moriya interaction results in the antiferro-type skyrmion crystal in an external magnetic field. We show that the antiferro-type skyrmion crystal turns into the ferro-type skyrmion crystal with the same topological charge for both layers when the magnitude of the external magnetic field is varied. We also demonstrate that the competing interactions between ordering wave-vector channels and their high-harmonic wave-vector channels are essential in stabilizing the antiferro-type skyrmion crystal. Our results provide important ingredients to realize the antiferro-type skyrmion crystal by the external magnetic field, which can be utilized for low-power and high-speed spintronic devices based on antiferromagnetic materials.

Investigation of the electronic, optical and magnetic properties of a novel two-dimensional lead-free perovskite: High visible-light absorption and long-range magnetic ordering.

Recently, big issues that need to be solved in photovoltaic solar cells area are the toxicity and instability of lead halide perovskites which have shown exceptional photoelectric performances. Herein, we report the synthesis and physico-chemical characterization of a novel two-dimensional (2D) lead-free perovskite. The 2D Cu(II)-based perovskite (C4N3H16)[CuCl4]∙Cl was successfully stabilized by the slow evaporation method under room temperature. The X-ray diffraction shows a layered structure with an inorganic network formed by four corners sharing CuCl6 octahedra. The UV-Vis absorption analysis confirms the manifestation of the cooperative Jahn-Teller effect around the Cu(II) ions. In addition to the ligand-to-metal charge transfer transitions, crystal field transitions (d-d) enhance the visible-light absorbance and make the material suitable for green solar cell applications with a band gap energy of 2.17 eV. The thermal analysis revealed the thermal stability of (C4N3H16)[CuCl4]∙Cl. Magnetic measurements revealed the presence of dominant ferromagnetic exchange interactions with J/kB = 22.85 K within the 2d planes, with a weak antiferromagnetic exchange interaction yielding a long-range magnetic ordering at 12 K.

Synthesis, crystal structure, magnetic behaviour and thermal stability of a paddle-wheel copper(II) complex bearing equatorial 3,4-diethoxybenzoate ligands.

The binuclear paddle-wheel copper(II) complex tetrakis(μ-3,4-diethoxybenzoato-κ2O:O')bis[(ethanol-κO)copper(II)], [Cu2(C11H13O4)4(C2H6O)2], has been synthesized and characterized. In each molecule, two CuII centres are bridged in a syn-syn fashion by four equatorial 3,4-diethoxybenzoate ligands, the two axial positions being occupied by ethanol molecules. The thermal stability has been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. The magnetic behaviour, studied by SQUID magnetometry, shows a CuII-CuII antiferromagnetic exchange interaction with 2J= -288 cm-1, a value that fits with a magnetic structure correlation established for compounds of this kind.

Copper (II) halide compounds with cationic N-donor ligands: Design, synthesis, structure and magnetism

Copper (II) complexes of the cationic ligands 1-(4′-pyridyl)-pyridinium (L1) and 1-(4′-pyridyl)-pyridin-4-ol (L2) have been prepared and characterized by single crystal X-ray diffraction and variable temperature magnetic susceptibility measurements: [Cu(L1)2X2]X2 [where X = Cl (1), Br (2)], and [Cu(L2)2X2]X2 [where X = Cl (3), Br (4)]. The complexes are fundamentally square planar with L2X2 coordination planes and long, semi-coordinate bonds to the additional halide ions. All compounds crystallize in monoclinic systems with 1 and 2 in the P21/n space group and 3 and 4 in the P21/c space group. The crystal structures are stabilized by both non-classical (in the case of 1 and 2) and classical (3 and 4) hydrogen bonds. EPR data for 1–4 support a rhombohedral structure, in good agreement with the local geometry as seen in the crystal structures. Magnetic susceptibility measurements show the presence of very weak antiferromagnetic interactions. In addition, the syntheses and magnetic properties of two neutral complexes, [Cu(L3)2X2]·2H2O [L3 = 1-(4′-pyridino)-4-pyridone; X = Cl (5), Br (6)] are reported. Magnetic susceptibility data indicate the presence of moderate antiferromagnetic exchange interactions [J ∼ 28 K (5), 60 K (6)] which were well modeled by the S = 1/2 Heisenberg uniform chain model.

Probing the weak limit of magnetocrystalline anisotropy through a spin‒flop transition in the van der Waals antiferromagnet CrPS4

The influence of magnetocrystalline anisotropy (MCA) on antiferromagnetism is elucidated through the characterization of the spin‒flop transition. However, due to a lack of suitable candidates for investigation, a detailed understanding of the preservation of the spin‒flop transition in the presence of low MCA energy remains elusive. In this study, we introduce CrPS4, which is a two-dimensional van der Waals antiferromagnet, as an ideal system to explore the exceedingly weak limit of the thermally-evolved MCA energy. By employing a uniaxially anisotropic spin model and fitting it to the experimental magnetic properties, we quantify the MCA energy and identify the discernible spin configurations in different magnetic phases. Notably, even at the limit of extremely weak MCA, with a mere 0.12% of the interlayer antiferromagnetic exchange interaction at T = 33 K, which is slightly below the Néel temperature (TN) of 38 K, the spin‒flop transition remains intact. We further establish a direct correlation between the visualized spin arrangements and the progressive reversal of magnetic torque induced by rotating magnetic fields. This analysis reveals the essential role of MCA in antiferromagnetism, thus extending our understanding to previously undetected limits and providing valuable insights for the development of spin-processing functionalities based on van der Waals magnets.

Facile synthesis of imidazolidinyl phenolate supported Dicopper(II/II) Complexes: Activation and fixation of atmospheric CO2 as MeOCO2− showing exogenous bridge modulating magnetic exchange coupling

Two imidazolidine grafted Schiff bases H3L2 and H3L3 have been utilized to fasten the Cu2 core in four new complexes [Cu2(μ-L2)(μ-O2CMe)]·H2O (1·H2O), [Cu2(μ-L2)(μ-O2COMe)]·H2O (2·H2O), [Cu2(μ-L2)(μ-NO3)]·H2O (3·H2O) and [Cu2L3(μ-OAc)]·5H2O (4·5H2O). Room temperature solution reaction of H3L2 with Cu2(OAc)4·2H2O provided 1·H2O in good yield. Follow-up reaction of 1·H2O with Et4NOH in air replaces μ-O2CMe (acetato) bridge by MeOCO2− (monomethyl carbonato) linker in 2·H2O. Single crystal X-ray structure established the individual complexes and confirmed the fixation of atmospheric CO2. Variable temperature (2 to 300 K) magnetic susceptibility measurements recognized the antiferromagnetic exchange interactions between the adjacent copper(II) centers in complexes 2 and 3. The amount of spin–spin interactions are found to be higher for ancillary NO3− bridge (−284 cm−1) compared to the in situ transformed MeOCO2− bridged (−1.64 cm−1).

The Nd-Fe-Rh system: Phase relations determination at 600 ℃ and magnetic property measurement of related compounds

The isothermal section of the Nd-Fe-Rh system at 600 ℃ was constructed based on the phase identification and analysis results from annealed alloys using X-ray diffraction and Scanning electron microscopy equipped with Energy dispersive spectroscopy. Two previously reported binary compounds, Nd4Rh and Fe2Nd, could not be confirmed. No new ternary compounds were found in the isothermal section. In the present work, the homogeneity ranges of the Fe-Rh binary system were redefined using phase disappear method, which were determined to be about 70–100 Fe at%, 51–69 Fe at%, 0–45 Fe at% for the single-phase region α-Fe, FeRh and γ-(Rh, Fe), respectively. It was confirmed that the maximum solid solubility of Fe in NdRh2, Nd3Rh and Nd7Rh3 is about 15.6 at% Fe, 4.0 at% Fe and 3.1 at% Fe, respectively, while no appreciable solubility was observed for the other binary compounds in the Nd-Fe-Rh system. The isothermal section of the Nd-Fe-Rh ternary system at 600 ℃ consists of 13 single-phase regions, 23 two-phase regions, and 11 three-phase regions. It suggests the presence of predominant antiferromagnetic exchange interaction in the NdRh compound. For the 38Nd-8Fe-54Rh sample, two magnetic entropy change peaks originate from the combined contribution from two magnetic phase transitions, an antiferromagnetic-paramagnetic transition and a ferromagnetic-paramagnetic transition for NdRh and NdRh2 phase, respectively.

Chemical pressure induced spin reorientation in the magnetic structure of Ca3Mn2−xSnxO7 ( x=0,0.03,0.05 )

The effect of partially substituting Tin (Sn) at the Manganese (Mn) site of Ca3Mn2O7 , viz. Ca3Mn2−xSnxO7 with x=0.03,0.05 , on its structural and magnetic properties have been investigated using synchrotron diffraction, neutron diffraction, and bulk magnetization measurements. It is observed that with a substitution of x=0.03 , the minor (≈8%) tetragonal ( I4/mmm ) structural phase that is present in the predominantly orthorhombic ( Cmc21 ) undoped Ca3Mn2O7 , completely disappears. The compounds order antiferromagnetically, the ordering temperature decreases with increasing Sn-content, indicating a weakening of the antiferromagnetic exchange interactions. Interestingly, in the ordered state, the spin magnetic moments which were aligned along the a-axis of the unit cell in the undoped compound, are observed to have reoriented with their major components lying in the b − c plane in the Sn-doped compounds. The above influence of Sn-doping is seen to be stemming from a significant modification of the octahedral rotation and tilt mode geometry in the unit cell, that is known to be responsible for driving ferroelectricity in these compounds.

Chinese-Lantern shaped [MnII2MnIII6NaI3] cluster assembled from Schiff base and azide bridges: Synthesis, magnetic study and catecholase-like activity

A multisite Schiff base, H2damp, derived from the condensation of o-vanillin and a sterically constrained amino-alcohol (2-amino-2-methylpropan-1-ol) was utilized to isolate a new mixed valence heterometallic complex [Na3MnIII6MnII2(damp)6(µ4-O)2(µ1,3-O2CCH3)2(µ1,1-N3)6(µ1,1,3-N3)(H2O)2]·5H2O·CH3OH (1). Room temperature reaction of H2damp in MeOH with Mn(II) acetate and NaN3 provided the complex having MnII2MnIII6NaI3 core. X-ray structure determination revealed the use of azide ancillary ligands for the growth of the complex on ligand-bound MnIII3O fragments. The variable temperature magnetic characterization of 1 revealed intramolecular anti-ferromagnetic exchange interactions. Complex 1 also showed catalytic property for the aerial oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) with a turnover number (kcat) of 392 h−1. EPR and mass spectrometric analysis established the probable mechanism of catalytic oxidase reactivity on the model substrate. In EPR study the characteristic peak at g ∼ 2 allowed us to spot the presence of an organic radical confirming the conversion of DTBCH2 to DTBQ in radical pathway.

Colossal Zero-Field-Cooled Exchange Bias via Tuning Compensated Ferrimagnetic in Kagome Metals.

Exchange bias (EB) is a crucial property with widespread applications but particularly occurs by complex interfacial magnetic interactions after field cooling. To date, intrinsic zero-field-cooled EB (ZEB) has only emerged in a few bulk frustrated systems and their magnitudes remain small yet. Here, enabled by high temperature synthesis, we uncover a colossal ZEB field of 4.95 kOe via tuning compensated ferrimagnetism in a family of kagome metals, which is almost twice the magnitude of known materials. Atomic-scale structure, spin dynamics, and magnetic theory revealed that these compensated ferrimagnets originate from significant antiferromagnetic exchange interactions embedded in the holmium-iron ferrimagnetic matrix due to supersaturated preferential manganese doping. A random antiferromagnetic order of manganese sublattice sandwiched between ferromagnetic iron kagome bilayers accounts for such unconventional pinning. The outcome of the present study outlines disorder-induced giant bulk ZEB and coercivity in layered frustrated systems.

Light-induced Kondo-like exciton-spin interaction in neodymium(II) doped hybrid perovskite

Tuning the properties of a pair of entangled electron and hole in a light-induced exciton is a fundamentally intriguing inquiry for quantum science. Here, using semiconducting hybrid perovskite as an exploratory platform, we discover that Nd2+-doped CH3NH3PbI3 (MAPbI3) perovskite exhibits a Kondo-like exciton-spin interaction under cryogenic and photoexcitation conditions. The feedback to such interaction between excitons in perovskite and the localized spins in Nd2+ is observed as notably prolonged carrier lifetimes measured by time-resolved photoluminescence, ~10 times to that of pristine MAPbI3 without Nd2+ dopant. From a mechanistic standpoint, such extended charge separation states are the consequence of the trap state enabled by the antiferromagnetic exchange interaction between the light-induced exciton and the localized 4 f spins of the Nd2+ in the proximity. Importantly, this Kondo-like exciton-spin interaction can be modulated by either increasing Nd2+ doping concentration that enhances the coupling between the exciton and Nd2+ 4 f spins as evidenced by elongated carrier lifetime, or by using an external magnetic field that can nullify the spin-dependent exchange interaction therein due to the unified orientations of Nd2+ spin angular momentum, thereby leading to exciton recombination at the dynamics comparable to pristine MAPbI3.

Strain-tuned incompatible magnetic exchange-interaction in La2NiO4

Magnetic frustration is a route for novel ground states, including spin liquids and spin ices. Such frustration can be introduced through either lattice geometry or incompatible exchange interactions. Here, we find that epitaxial strain is an effective tool for tuning antiferromagnetic exchange interactions in a square-lattice system. By studying the magnon excitations in La2NiO4 films using resonant inelastic x-ray scattering, we show that the magnon displays substantial dispersion along the antiferromagnetic zone boundary, at energies that depend on the lattice of the film’s substrate. Using first principles simulations and an effective spin model, we demonstrate that the antiferromagnetic next-nearest neighbour coupling is a consequence of the two-orbital nature of La2NiO4. Altogether, we illustrate that compressive epitaxial strain enhances this coupling and, as a result, increases the level of incompatibility between exchange interactions within a model square-lattice system.

Tailoring Bi1−x−yBaxFeyFeO3 for desired properties: insights into structural, dielectric, and magnetic responses

In present study, samples of Bi1−x−yBaxFeyFeO3 have been synthesized, where x = 0.15, y = 0; x = 0.10, y = 0.10; and x = 0.15, y = 0.10 utilizing a swift two-stage solid-state reaction method. X-ray diffraction (XRD) data has been Rietveld refined to evaluate the structural parameters. Micro-strain is also calculated using Williamson Hall method. Temperature (300 K to 660 K) dependent measurements of the dielectric constant have been conducted at various frequencies (100 kHz, 500 kHz, and 1000 kHz). The dielectric constant (ε′) rises as the temperature increases. Two dielectric anomalies around 450 K and 613 K have been noticed in ε′ versus T curves for all the samples which might be related with defect dipoles and the magnetic transition respectively. Further, an insignificant value of loss tangent (0.2) specifically at around 300 K is a signal of small leakage current in the samples. The source of high dielectric constant is discussed by considering the structural distortions in the ceramics. A clear hysteresis loop has been observed for all the samples which is a sign of collapse of antiferromagnetic nature of BiFeO3. Further, in case of co-doped samples, almost a saturation in magnetization with magnetization value 5.9718 emu g−1 has been noticed in hysteresis curve indicating a major contribution of ferromagnetic interaction. Enhancement in the net magnetization is briefly discussed by considering the ferromagnetic type direct interaction among Fe3+ ions and suppressing the anti-ferromagnetic type super exchange interaction.

Gd3+ based spin [formula omitted] linear chain antiferromagnet

We report observations of spin 12 Heisenberg antiferromagnetic order in nanoparticle ensembles of Gd1.89Ni0.02Zn0.03Fe0.55O4 and Gd1.39Ni0.10Zn0.02Fe0.89O4. The staggered molar susceptibility, χm(T), of the ensembles varies as 1/T as T→TN≈17 K. Below TN, the χmT is directly proportional to the temperature before showing another upturn. An excellent agreement between the experimental χm(T) and theoretical models (Bonner-Fisher and Eggert) confirms spin 12 antiferromagnetic coupling within the linear chains of electron spins of the ensembles. The exchange constant is JkB=17K. The antiferromagnetic exchange interaction is also signified by a constriction at the middle of the hysteresis loop, at H=0, which becomes narrow at 5 K. We argue that the origin of the exchange interaction is in the quantum interference of the Bloch waves with the composite energy states of the domain walls.